I'd say it's not impossible but much more difficult.
Remember that what swung Florida to Trump was primarily the suburban/exurban counties immediately north of the core I-4 corridor. This area has many people who formerly resided in the Rust Belt. Thus, if the next Democratic nominee can flip FL, in all likelihood he or she is also able to flip at least one of the three decisive Rust Belt states (WI, MI, and/or PA). If FL flips to D, only one of those three Rust Belt states would be necessary for a Democratic victory; without FL, all three would be necessary.
